This invention relates to a vehicle shock absorber, and particularly to a means for dampening the action of vehicle's suspension travel.
The novel concept of this invention adopts functions similar to those of the dampening shock absorber described and claimed by the present inventor in his Christopherson U.S. Pat. No. 4,736,931. As disclosed therein, the shock absorber configuration provided a retrofit of a spring assembly to a conventional gas charged or hydraulic shock or strut that involved an outer sleeve telescoped over an inner sleeve containing a piston movable against hydraulic or gaseous resistance. The patented spring assembly consists of a coil spring surrounding a tubular sleeve in telescoping relationship with a conventional tubular shock absorber configuration, a pair of oppositely disposed longitudinal grooves in the outer tubular sleeve, and oppositley disposed pairs of spring retaining clips each having inwardly projecting bosses or fingers slidably received by the respective grooves, and further including outwardly extending flanged areas arranged to receive the coil spring. Longitudinally spaced retaining rings are each secured around the inner shock absorber sleeves to act as stops for the respective spring retainer clips. Another embodiment of the patent provides an adjustable collar positioned between a retaining clip and its end of the coil spring. The spacing between retaining clips may thereby be changed to provide preload adjustment of the compressive force exerted by the coil spring against the collar.
It has been observed that the primary factor in vehicle ride control is the vehicle spring rate. Spring rate has been defined as pounds/deflected inch. Using coil suspension for purposes of illustration, a soft spring would need to be deflected more than a stiff spring to support a given vehicle weight. Consequently, a soft spring has a longer free length than a stiff spring. When two identical vehicles of equal ride height are compared, soft springs on one and stiff springs on the other, the ride height will be maintained with both vehicles being driven in a straight line on level pavement. However, under roll and pitch conditions, control would be better in the stiffly sprung vehicle, because stiff springs unload sooner.
For a better understanding, specific terminology has been used for purposes of the following discussion. "Roll" refers to tilting of the vehicle's sprung mass (passenger space and vehicle body) when cornering. Roll is caused by the extension and/or compression of the vehicle's main suspension springs above or below resting ride height (equilibrium). Equilibrium, in this case, being the neutral resting ride height resulting from the weight of the sprung mass (passenger, cargo, body, trim, etc.) as supported by suspension springs. Roll has traditionally been controlled by so-called sway bars. "Pitch" refers to rocking the vehicle front to back. This is usually caused by road anomalies. Pitch has traditionally been controlled by conventional shock absorbers. Sway bars have no effect on pitch. "Float" or "bounce" refers to undesirable extension of the suspension system past normal ride height. This condition is also caused by road anomalies. Here again, sway bars have no effect on control of the vehicle.
Standard shock absorbers without "negative boost" allow the center of gravity to shift to an angle which may cause discomfort to the driver and passengers, and materially affect control of the vehicle. This shift is particularly true during a roll while the vehicle is cornering. In a vehicle such as a van or step-van emergency medical transport, where the center of gravity is relatively high, roll may interfere with the attempts to stabilize emergency patients. Rollovers have been known to occur during cornering, where vehicle suspension has not been considered carefully. Two factors are responsible for this condition. The most obvious factor--stiff springs support more weight in a given amount of spring travel than do soft springs. This condition, for example, will occur on the outside of a turn. The less obvious factor lies in the fact that, since soft springs have a longer free length, they will continue to lift more when cornering. This condition occurs on the inside of a turn.
It will be apparent that the distance traveled by the load to reach equilibrium is greater in a soft sprung vehicle than in a stiffly sprung vehicle. The travel distance required to load the springs (suspend) is the greatest factor in most ride control problems relating to pitch, roll or float conditions.
The improved dampening shock absorber of this invention provides a neutral zone travel area affording a softer ride during straight road cruising on a level surface. The improvement also provides negative boost (pull-down) to the shock absorbers when the vehicle (sprung mass) tends to lift beyond resting ride height, i.e., during cornering wherein the inside springs unload, lifting the vehicle (sprung mass) while the outside springs compress below resting ride height. The opposite action occurs during positive boost (pushup) of the dampening feature of the invention wherein the vehicle's suspension compresses below a pre-established neutral zone travel.
Shock absorbers with dampening features further contribute towards compensation for uneven load suspension distribution caused by applying trailer hitch loads. In such case, the rear suspension is subjected to forces causing the front end of the vehicle to lift and thereby allow the front springs to lift the vehicle (sprung mass) above resting ride height. At the same time, the load on the rear wheel suspension is increased, thereby lowering the vehicle (sprung mass) to a position below resting ride height.